This invention relates to a control system for a mineral mining installation, and to a mineral mining installation employing such a system.
In mineral mining installations employing a mineral winning machine movable along a guide, it is known to provide a control system for operating shifting rams to cause the guide, and hence the winning machine, to be advanced towards the mineral face. The guide is either formed on one side of a lonwall scraper-chain conveyor or is a separate guideway associated with the conveyor. The guide is usually composed of sections and it is conventional to cause the guide sections to be advanced successively and incrementally by the full cutting depth of the machine after passage of the machine. Each guide section is provided with a shifting ram, and the shifting rams abut against the units of a walking frame roof support assembly. The shifting rams are, therefore, used for advancing the guide, the conveyor and the winning machine after the winning machine has cut away the mineral face to its full depth, as well as for applying a regulated thrust to the guide, and hence to the winning machine, during the winning process. This regulated thrust is controlled, in the known control system, by control valves provided in the hydraulic distribution system leading to the rams and extending along the longwall conveyor. The hydraulic distribution system also supplies other devices such as the props of the roof support assembly.
The shifting rams are also used for drawing up the units of the roof support assembly after the guide, conveyor and winning machine have been advanced. Since higher pressures are needed for this advancement of the roof support assembly, the pressure applied by the winning machine, via the guide and the shifting rams, is often unnecessarily high. These excessive pressures are sometimes even harmful, because the power consumption of the drive for the winning machine is substantially increased. Where, as is usual, the winning machine is chain driven, the excessive thrust may, even during normal operations, cause snapping of the safety shear pins which serve to limit the tension in the chains. Moreover, unnecessarily high thrust applied to the winning machine results in excessive wear to its cutters and sometimes to jamming of the machine.
These difficulties are particularly prevalent where the winning machine is a plough which is movable along a guide formed on the conveyor and which is driven, via a sword plate extending under the conveyor, by an endless chain provided on the goaf side of the conveyor. This is because the reaction forces of the plough act to force the conveyor away from the face so as to cause high pressure in the rams which thus consume a high proportion of the overall power consumption. Moreover, in order to prevent jamming of the plough, it is necessary to use heavy duty machinery and thick driving chain for the plough.